1. Field of the Invention
This invention relates generally to the field of variable resistance devices and more particularly to ratcheting mechanisms for worm gear actuated potentiometers.
2. Description of the Prior Art
Worm gear actuated potentiometers are well-known in the art and have been for some time. A common problem encountered in the construction of devices of this kind is in the method of provision of means by which excessive rotation of the driving element can be accommodated without damage to internal elements. In most applications it is necessary to provide a stop so as to prevent the contact from being rotated through an indefinite number of rotations. Lacking such a stop provision, the resistance ratio may suffer discontinuous changes as a result of the travel of the wiper into and through open circuit conditions. In many prior art worm gear actuated potentiometers, positive stops were provided which prevented the wiper from rotating through such a distance as to lose contact with the resistance element. These stops solved the problem of discontinuous change of the resistance ratio by limiting the wiper travel, however, another problem was thus generated. In the early prior art worm gear actuated potentiometers, continued rotation of the drive screw after a limit stop was reached would cause stripping of the gears on the driven rotor carrying the wiper, thus causing destruction of the device. This was a very frequent occurence since the interior of the worm gear actuated potentiometer was not usually visible to the operator. In some of the later devices, friction clutch means were employed such that when the wiper reached a limit stop, the friction means would allow slippage so as not to damage the interior elements as a result of excessive rotation of the driving screw. Some of these devices, however, also allow slippage under conditions that the wiper has not reached a limit stop and thus operation becomes erratic and unreliable. Various ratcheting devices have subsequently been employed in attempts to solve the problem presented. Most have either presented new problems or only partially solved the problem presented. Most of these devices have thus met special needs as presented by specific problems and have therefore served narrow purposes. These prior art devices, among other disadvantages, have required separate stop mechanisms in addition to the ratcheting mechanism, have been unreliable and unpredictable in operation under continued use and have been expensive and complicated to manufacture. Some of these prior art devices have been described in the following listed patents that were brought to the attention of the applicant through a novelty search conducted in the United States Patent and Trademark Office:
1. No. 3,497,856 -- "Adjustable Potentiometer" -- L. W. Scheel PA1 2. No. 3,242,452 -- "Clutch Means for Multiple Turn Variable Resistor" -- A. A. Grunwald, et al. PA1 3. No. 3,768,325 -- "Multiturn Adjustment Potentiometer Ratcheting Mechanism" -- L. Kucharski, Jr. PA1 4. No. 3,683,308 -- "Potentiometers" -- A. L. Hamill PA1 5. No. 3,569,896 -- "Ultrathin Miniature Potentiometer with Recessed Drive Means" -- W. D. Kirkendall PA1 6. No. 3,522,573 -- "Potentiometer Shaft Retention" -- R. D. Michik PA1 7. No. 3,522,572 -- "Gear Adjusted Potentiometer" -- R. D. Michik PA1 8. No. 3,208,024 -- "Potentiometer Construction" -- H. B. Enos et al. PA1 9. No. 3,099,810 -- "Miniature Potentiometer" -- H. Habereder PA1 10. No. 3,416,119 -- "Variable Resistance Control with Clutch Mechanism" -- J. Van Beuthuysen PA1 11. No. 3,115,614 -- "Miniature Potentiometer with Stop Mechanism" -- H. Habereder PA1 12. No. 3,701,070 -- "Worm Gear Actuated Potentiometer" -- K. B. Baldwin et al. PA1 13. No. 3,582,857 -- "Worm Driven Adjustable Potentiometer" -- J. F. Kishel PA1 14. No. 3,639,878 -- "Adjustable Potentiometer with Contactor Ratchet and Central Post Securing Means for Baseplate" -- L. W. Scheel PA1 15. No. 3,478,294 -- "Variable Resistor" -- W. D. Kirkendall PA1 16. No. 3,446,085 -- "Variable Resistor" -- L. Ginsberg PA1 17. No. 3,384,851 -- "Gear Adjusted Potentiometer" -- W. H. King PA1 18. No. 3,378,803 -- "Variable Resistance Potentiometer" -- C. Yungblut et al.
It would thus be a great advantage to the art to provide an improved ratcheting mechanism for a worm gear actuated potentiometer;
It would be another great advantage to the art to provide an improved ratcheting mechanism for a worm gear actuated potentiometer which is simple and inexpensive to manufacture;
A further desirable advantage to the art would be to provide a ratcheting mechanism for a worm gear actuated potentiometer which is predictable and reliable;
A still further desirable advantage to the art would be the provision of a worm gear actuated potentiometer having a ratchet member and a drive member that are urged into engagement through the action of a commonly presently employed element;
It would also be great advantage to the art to provide a worm gear actuated potentiometer showing the advantages of ratcheting to prevent interior damage to the elements that will have a long operating life.